Karl Hermann Gustav Müller (7 May 1851–7 July 1925) was a German astronomer. He was born in Schweidnitz,

Silesia Silesia (see names #Etymology, below) is a historical region of Central Europe that lies mostly within Poland, with small parts in the Czech Silesia, Czech Republic and Germany. Its area is approximately , and the population is estimated at 8, ...

to a merchant father; his father died when Gustav was six. In 1870 he entered the

University of Leipzig Leipzig University (), in Leipzig in Saxony, Germany, is one of the world's oldest universities and the second-oldest university (by consecutive years of existence) in Germany. The university was founded on 2 December 1409 by Frederick I, Electo ...

, then transferred to the

University of Berlin The Humboldt University of Berlin (, abbreviated HU Berlin) is a public research university in the central borough of Mitte in Berlin, Germany. The university was established by Frederick William III on the initiative of Wilhelm von Humbol ...

two years later. He was awarded a Ph.D. in 1877 with a thesis on the subject of micrometer screws. Thereupon he became an assistant at the

Astrophysical Observatory of Potsdam Leibniz Institute for Astrophysics Potsdam (AIP) is a German research institute. It is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Institute Potsdam#Foundation of the Astrophysical Observatory Potsdam .28AOP. ...

. His primary career focus became the spectrum of the Sun and celestial photometry. Between 1880–82, he assisted

Hermann Carl Vogel Hermann Carl Vogel (; ; 3 April 1841 – 13 August 1907) was a German astrophysicist. He was born in Leipzig, Kingdom of Saxony. From 1882 to 1907 he was director of the Astrophysical Observatory, Potsdam. He made extensive discoveries ...

in building a catalog of

stellar spectra Astronomical spectroscopy is the study of astronomy using the techniques of spectroscopy to measure the spectrum of electromagnetic radiation, including visible light, ultraviolet, X-ray, infrared and radio waves that radiate from stars and othe ...

. In 1877 he began making photometric observations of the planets and their atmospheres. He led the German expedition to

Hartford, Connecticut Hartford is the List of capitals in the United States, capital city of the U.S. state of Connecticut. The city, located in Hartford County, Connecticut, Hartford County, had a population of 121,054 as of the 2020 United States census, 2020 ce ...

, to observe the

transit of Venus A transit of Venus takes place when Venus passes directly between the Sun and the Earth (or any other superior planet), becoming visible against (and hence obscuring a small portion of) the solar disk. During a transit, Venus is visible as ...

in 1882. In 1886, he began a collaboration with Paul Kempf to assemble the ''Potsdam Durchmusterung'', which was a stellar catalogue of all stars in the northern hemisphere with a magnitude of 7.5 or brighter. In 1897 he published the manual ''Die Photometrie der Gestirne'' (The Photometry of Stars). Between 1900 and 1915, he and Hartwig produced a three volume catalogue of 1,687

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

s. Between 1896 and 1924, he served as a secretary of the ''

Astronomische Gesellschaft __NOTOC__ The ''Astronomische Gesellschaft'' is an astronomical society established in 1863 in Heidelberg, the second oldest astronomical society after the Royal Astronomical Society. History In 1882, the ''Astronomische Gesellschaft'' founded t ...

''. In 1918 he was elected to the

Prussian Academy of Sciences The Royal Prussian Academy of Sciences () was an academy established in Berlin, Germany on 11 July 1700, four years after the Prussian Academy of Arts, or "Arts Academy," to which "Berlin Academy" may also refer. In the 18th century, when Frenc ...

, and he would also become an associate of the

Royal Astronomical Society The Royal Astronomical Society (RAS) is a learned society and charitable organisation, charity that encourages and promotes the study of astronomy, planetary science, solar-system science, geophysics and closely related branches of science. Its ...

in England. From 1917–1921 he was the director of the Astrophysical Observatory at Potsdam. Due to legal requirements, he retired in 1921 at the age of seventy. He was married three times and had seven children. One son was killed during

World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

and a second in the aftermath. His son Rolf became an astronomer at the

Potsdam Observatory Leibniz Institute for Astrophysics Potsdam (AIP) is a German research institute. It is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory Potsdam (AOP) founded in 1874. The latter was the world's first ...

References

{{DEFAULTSORT:Muller, Gustav 1851 births 1925 deaths 19th-century German astronomers Astronomers from the Kingdom of Prussia Humboldt University of Berlin alumni Leipzig University alumni People from Świdnica 20th-century German astronomers Members of the Royal Society of Sciences in Uppsala